1. Field of the Invention
The present invention relates to a process for obtaining hirudin derivatives from E. coli secretor mutants, and to a hirudin derivative with the N-terminal amino-acid sequence (SEQ ID NO: 1).
2. The Prior Art
Hirudin is a polypeptide with 65 amino acids and was originally isolated from the leach Hirudo medicinalis. It acts as a highly specific inhibitor of thrombin by forming stable complexes with thrombin and, therefore, has many possible therapeutic uses, especially for anticoagulation therapy (F. Markquardt, Biomed. Biochim. Acta 44 (1985), 1007-1013).
The publication of the complete amino-acid sequence of hirudin (J. Dodt et al., FEBS LETTERS 165 (2), (1984), 180-184) was the prerequisite for the preparation of hirudin by recombinant DNA techniques and expression in microorganisms.
European Patent Application No. 158,564 (Transgene) discloses cloning vectors for the expression of hirudin or hirudin analogues in a host cell, especially a bacterial cell. The gene coding for hirudin is, in this case, obtained by cDNA synthesis starting from mRNA from the leach Hirudo medicinalis. Described, in particular, is a hirudin derivative with the N-terminal sequence (SEQ ID NO: 2) and processes for obtaining it.
European Patent Application No. 168,342 (Ciba Geigy) discloses DNA sequences which code for the natural amino-acid sequence of hirudin, wherein the N-terminal amino-acid sequence is (SEQ ID NO: 3). The expression of hirudin takes place intracellularly in the microorganisms E. coli and Saccharomyces cerevisiae.
European Patent Application No. 171,024 (Hoechst AG) discloses a process for the genetic engineering for preparation of polypeptides with hirudin activity, in particular, in E. coli cells, wherein the cells are disrupted and the polypeptide with hirudin activity is obtained from the cell extract. A fusion protein portion which is present where appropriate can be deleted by proteolytic or chemical cleavage, and the liberated hirudin molecule can be purified.
German Patent Application No. 3,445,571 (GEN-BIO-TEC) relates to a DNA sequence which codes for a protein with the biological activity of hirudin, and to a process for obtaining such proteins from E. coli cells which are transformed with a suitable recombinant vector by lysis of the cells.
The paper by Bergmann et al (Biol. Chem. Hoppe Seyler 367 (1986), 731-740) also describes hirudin synthesis in E. coli. The hirudin is released from the cells by toluene treatment, with only low yields of about 500 ng/l A.sub.578 units of cells being achieved.
European Patent Application No. 200,655 (Transgene), European Patent Application No. 252,854 (Transgene), and European Patent Application No. 225,633 (Ciba Geigy) disclose the obtaining by secretion of proteins with hirudin activity from a eukaryotic host organism, especially yeast, wherein the expression takes place on a vector which contains a DNA sequence which contains a signal peptide upstream of the structural gene. The secretion of hirudin derivatives with the N-terminal sequence (SEQ ID NO: 3) and with the N-terminal sequence (SEQ ID NO: 2) in yeast is disclosed. In this case, yields of up to 100 mg/l are reported.
German Patent Application No. 3,900,626 (Hoechst AG) discloses a hirudin derivative with the N-terminal sequence (SEQ ID NO: 4). The expression takes place preferably in yeast, using the promoter and signal sequence of the yeast pheromone gene MF.alpha. for the expression and secretion of the hirudin derivative.
All the processes described above for preparing hirudin derivatives have disadvantages, however. Thus, when yeast is used as the host organism, and the hirudin is secreted into the culture medium, relatively high yields are obtained, but the cultivation of yeast cells takes longer and is more demanding than that of bacteria, for example, E. coli. However, on the other hand, in E. coli cells, the yield is relatively low, and/or complicated isolation processes are necessary on disruption of the cells.